Of course, if people didn't have accounts with 10 different OpenID providers in the first place, they wouldn't have to remember which one they used. It seems like many big sites opted to become a provider rather than start accepting logins from existing providers, for which I suppose I can't blame them.

Why not blame the bigger sites? If they accepted logins from other OpenID providers, then people would have a lot fewer possibilities to remember. I honestly believe this is a big part of the problem with OpenID adoption currently.